Electrical apparatus



July 24, 1962 B. A. RITZENTHALER ELECTRICAL APPARATUS Filed Dec. 31, 1958 INVENTOR.

Bruce A Rifzenfhaler ATTORNEY United States aten 3,046,420 ELECTRICAL APPARATUS Bruce Allen Ritzenthaler, Chicago, Ill., assignor to Standard Oil Company, Chicago, Ill., a corporation of Indiana Filed Dec. 31, 1958, Ser. No. 784,311 7 Claims. ((11. 307-132) This invention relates to relay pulsing circuits, and more particularly is concerned with providing means for generating a cyclically repetitive pulse with apparatus which is characterized in having extremely long component life.

In certain electrical testing and measuring applications it is desired to produce a pulsating on-off current with the pulsations occurring at a frequency in the range of about 0.1 to about 60 cycles per second. This frequency range is, in general, too low to permit the use of electron tube vibrators, and as a consequence it becomes necessary to rely on conventional electromechanical relay pulsing circuits. These circuits employ an armature which functions as an interrupter in the power line of a relay coil. A capacitance is in shunt around the coil to prevent highvoltage arcing at the contacts. With relay pulsing circuits however, the requirement that the armature have a short period of vibration, or in other words be small in size and light in Weight, frequently mitigates against extended life of the armature and the contact points. Since these circuits often must operate over many millions of cycles, it is evident that suitable means must be provided for securing adequate component life.

It is well known that a condenser in series with a resistance bridged about a contact is an effective method for eliminating or reducing high temperature arcs formed upon making or breaking an electrical contact. It has also been proposed heretofore that various other combinations of condensers and resistances may be employed for this service. Unfortunately, the protective networks in the prior art are not suitable for use with relay pulsing circuits in which a capacitance is in shunt with the relay coil, since the circuit is already capacitive and high voltage arcing is therefore not a problem. The cause of arcing in these circuits is low contact pressure and slow armature travel.

It is therefore an object of the instant invention to provide an improved relay pulsing circuit having high contact pressures and rapid armature travel to reduce arcing and furnish exceptionally long contact life. A further object is to provide a simple and rugged pulsing circuit in which means are provided for regulating the pulse frequency. An additional object is toprovide a relay pulse circuit for generating pulses in the 0.1-60 cycles per second range. Yet another object is to provide a relay pulsing circuit with fixed or variable control over the portion of time during which the relay remains open or closed. Other and more particular objects will become evident as the description of the invention proceeds.

In accordance with the objects above, a relay pulsing circuit having a conventional capacitance shunted around the relay coil is provided with a low-resistance discharge path to discharge the capacitance when the armature is in the normally-open position, and with a high resistance path bridged across the normally-closed contact position. The low-resistance discharge path, by governing the rate at which the capacitance discharges, controls the time during each cycle when the relay is closed. The high resistance path which is bridged across the normally-closed contact provides additional current in the relay coil to assure that the normally-closedcontact is broken so rapidly that the tendency of the normally-closed contact points to are is greatly reduced. Current flowing to the relay coil through this resistance also increases the contact pressure between the armature and the normallyopen contact so that arcing at the latter is similarly minimized.

The invention will be more fully described with reference to the attached figure.

The relay pulsing circuit of the instant invention which activates armature 13 may be supplied with either alternating or direct current. In the drawing as shown, the current supply is volts A0. at 60 cycles per second supplied through connections 1 and 2. Switch S-1 turns the unit on or off. To rectify this alternating current a selenium type half wave rectifier 3 is provided, along with a series current-limiting resistor R and condenser C in shunt across the power line at connections 4 and 10. Current to energize relay coil 5 flows through the circuit comprising fixed resistor R variable resistor R line 19, normally closed contact 8, spring biased armature 7, connection 18, and thence through coil 5. Relay coil 5 desirably has a centrally disposed low-hysteresis iron core 6 by means of which magnetic flux created by coil 5 is concentrated and acts to drive armatures 7 and 13. Condenser C is in shunt around relay coil 5. Resistor R is connected from connection 10 to normallyopen contact point 9, while resistor R is connected from connection 18 at armature 7 to line 19. It will be observed that when armature 7 is in normally closed position, power supplied to relay coil 5 is shorted around resistance R and hence the full current is applied to the coil. When armature 7 is in normally open position, resistance R is then connected in parallel with relay coil 5 and with condenser C so as to cause the latter to discharge through R An external load circuit in which pulsations may also be formed is represented by terminals 16 and 17 or 17 and 20. When armature 13 is in the normally-closed position no current can flow through the former load circuit, while when armature 13 is in the normally open position, i.e. at contact point 15, current is permitted to flow in this circuit.

To provide an optional but highly desirable visual signal to indicate each pulsation, a neon bulb 21 is connected in parallel with resistor R both of these being nected in parallel with resistor R This circuit is connected between connections 4 and 18.

The operation of the present relay pulsing circuit may be described as follows. When switch 8-1 is closed so as to supply power to the relay pulsing circuit, condenser C charges through selenium rectifier 3 and through current limiting resistor R to about -160 volts DC. This direct current is ultimately applied to relay coil 5. Positive current at connection 4 flows through fixed resistor R and variable resistor or potentiometer R and thence through normally closed contact 8, armature 7, and connection 8 to shunt-connected relay coil 5 and condenser C The rate at which current is supplied to this latter shunt combination may be varied by appropriate adjustment of variable resistor R reducing the value of resistance across resistor R increases the pulse generation rate. Resistor R is provided to insure that an exces' sive pulse rate is not attained.

When the voltage across condenser C reaches about 50 volts, the current through relay coil 5 is then sutlicient to energize armature 7 and move it from normally closed contact 8 to normally open contact 9. Immediately upon disengagement of armature 7 from normally closed contact 8, and before normally open contact 9 is contacted, condenser C commences to discharge back through relay coil 5. This discharge action serves to rapidly remove the magnetic field created by coil 5 and iron core 6. When, after a period of a few milliseconds, armature 7 contacts normally open contact 9, an additional discharge path for aoeaeao condenser C is provided by way of resistance R Resistance R is connected to normally open contact 9 and bridged about condenser C It is apparent, then, that when normally open contact 9 is engaged, condenser C discharges more rapidly than during the brief period when armature 7 is being repositioned.

The fraction of time during which normally open contact 9 is engaged is regulated by the value of resistance R Resistance R may be a fixed resistor, in which event the relay closed time is relatively constant at all pulse frequency rates. However, where it is desired to vary the time during each cycle when the relay is in normally open (or normally closed) position, resistor R may comprise a variable resistor or potentiometer. Without the employment of resistor R a cyclic relay pulse rate of only 2 to about a maximum of about 10 cycles per second can be attained, while with the additional capacitancedischarge circuit provided by resistor R the maximum cyclic rate is increased to about 60 or more cycles per second.

When the voltage across condenser C falls to about 11 volts, a spring or (less desirably) gravity bias on armature 7 exerts a physical force which, at the low voltage, is effective to return armature 7 from normally open contact 9 to normally closed contact 8.

The above completes one cycle of operation. Another cycle begins immediately since condenser C begins charging as soon as armature 7 returns to normally closed contact 8.

The circuit as described above, without resistance R is eifective in generating relay pulses without further modification. However, it has been found experimentally that apparatus lacking resistance R will function for only a few thousand cycles, whereupon pitting occurs where armature 7 touches normally open contact 9 and normally closed contact 8. It has been discovered in further accordance with the invention that the high-resistance R circuit bridged around normally closed contact 8 not only increases contact life well beyond several million cycles, but also provides additional flow-in current for coil 5 to assure that normally closed contact 8 is broken swiftly. It also reduces the in transit time for armature 7 to travel between normally-closed contact 8 and normally open contact 9. Lastly, it establishes greater contact pressure between armature 7 and normally open contact 9 These three conditions contrive to make and break the respective contacts very rapidly and assure strong contact pressures, thus providing extraordinarily long contact life.

Resister R functions in the circuit when the voltage across condenser C reaches about 50 volts and relay coil 5 starts to reposition armature 7 from normally closed contact 8 to normally open contact 9. During the in transit time when neither contact is engaged, in the absence of resistance R the only current flowing through relay coil 5 would be the current provided by discharging condenser C However, with the high resistance circuit provided by resistance R additional current from the power source is applied to coil 5 so as to increase its magnetic strength. This increased power to relay coil 5 provides a clean swift break of normally closed contact 8 and in addition provides greater normally-open contact 9 pressure during the initial heavy current discharge of condenser C As shown in the drawing, the relay pulse circuit may be operatively connected to a second armature, armature 13, which is alternately positionable between normallyclosed contact 14 and normally open contact in a circuit which is preferably independent electrically but dependent magnetically on the relay pulse circuit. Dashed line 12 illustrates this magnetic dependency. In the same manner dashed line 11 represents the magnetic dependency of the first armature 7 at coil 5 and core 6. Armatures 7 and 13 may be either mechanically dependent or independent of each other provided they both are driven by the action of coil 5. The second armature 13 is connected into an external load circuit via terminals 16 and 17 or 17 and it so that armature 13 follows the positioning of armature 7 and thereby opens and closes the second armature 13 in synchronization with first armature 7.

The relay pulsing circuit described herein has numerous applications either by itself or in combination with other electrical apparatus. It may for example be employed as a pulse generator for stepper-relay sampling systems; as a pulse generatorfor testing nuclear decade-type counters, linear amplifiers and counting rate meters; for standardizing timing apparatus; and for other applications in which an intermittent circuit (with or without variable rate) is desired. The circuit may also be used Without making or breaking electrical load circuits, and an illustration of this is an electrical metronome where the audible click of armature 7 provides the necessary sound. It has been found that the relay pulse circuit has been especially effective in testing wild ping counters. Wild ping is a phenomenon which occurs in internal combustion engine cylinders by combustion chamber deposits randomly igniting the gas-fuel mixture before the spark plug fires. Wild ping counters are somewhat sensitive and must be calibrated frequently; the instant relay pulsing circuit is used for generating a standard frequency pulse which is fed to the input of wild ping counter while a visible comparison is made of blinking lights on the relay pulse circuit and on the counter.

As an example of a relay pulser according to the invention, the following specific values of resistances and capacitances for a suitable pulse circuit are listed below.

TABLE I Resistances R 22 ohms /2 w. R 470 ohms 1 w. R, 20 k. 2 w. R, 56 k. 1 w. R 200 k. 10 w. R 2.7 k. 1 w.

TABLE II Condensers C -30 microfarad, volt C .40 microfarad, 150 volt D.C.

From the above description, it is manifest that a relay pulsing device according to the above description fully satisfies the objects of the invention. With this device, pulse frequencies in the range of about 0.1 to 60 or more cycles per second may be conveniently established while component lifeespecially contact point lifeis increased from the 5000 or 6000 cycles heretofore obtainable to an indefinite life in excess of 5 million cycles. The provision of a low resistance discharge path connected to normally open contact 9 permits higher pulse frequencies than can be attained without this path. Moreover, the inclusion of a high resistance path bridged about normallyclosed contact 8 serves to rapidly make and break electrical contacts between armature 7 and the respective contact points 8 and 9.

It is also apparent that many variations of the inventive circuit may be made within the scope of the appended claims. For example, resistance R may be responsive to an independent variable, such as a thermistor responsive to ambient temperature, and thereby furnish a pluse cycle having a dependently variable normally-open or normally-closed time. Similarly, resistance R may be used to regulate the pulse rate in response to, say, the wiper position of a temperature or pressure indicator.

I claim:

1. An improved electromagnetic relay pulsing circuit which comprises: a relay coil and means for supplying power thereto, a first armature driven by said coil and being alternately movable between normally-open and normally-closed contacts in the power supply means, a

second armature driven by said coil and connected in a a first discharge path including a low resistance connected to discharge said capacitance means through said normally-open contact whereby the portion of time when the first armature is engaged with the normally-closed contact is controlled, and a second discharge path including a high resistance bridged across the normally-closed contact topermit the application of power to said relay coil when said first armature is in the normally-open position and thereby provide rapid opening of the normallyclosed contact and increase the contact pressure at the normally open contact.

2. Circuit of claim 1 including means for adjusting the power supplied to said relay coil.

3. Circuit of claim 1 including means for indicating each pulsation of the circuit.

4. An improved electromagnetic relay pulsing circuit, such circuit having a relay coil, a capacitance in shunt with said coil, power supply means and an interrupter armature in said circuit, said interrupter armature being movable between normally open and normallly closed contacts, the circuit comprising in combination means varying said power supply to produce pulses in the range of about 0.1 to about 60 cycles/sec, a low resistance path discharging the capacitance through said normally open contact whereby the portion of time when the armature is engaged with the normally closed contact is controlled, and a high resistance path bridged across the normally closed contact to provide rapid disengagement from the normally closed contact, said high resistance path permitting the application of power from said power supply means to said coil when said interrupter armature is in the normally open position whereby contact pressure is increased at the normally open contact.

5. In a circuit comprising a relay coil, an armature in circuit with, and actuated by, said relay coil, said armature being alternately movable between normally-open and normally-closed contacts, and capacitance means in shunt relationship with said relay coil, the improvement comprising a low resistance discharge path connected to discharge said capacitance means through the normallyopen contact and thereby control the portion of time when said armature is in the normally-closed position.

6. Circuit of claim 5 including a high resistance path connected through the normally-open contact to provide rapid opening of the normally-closed contact and to increase contact pressure at the normally-open contact, whereby improved contact life is achieved.

7. In an electromagnetic relay pulsing circuit having a relay coil, an interrupter in the power supply to said coil, said interrupter being alternately movable between normally-open and normally-closed contacts, and capacitance means in shunt around said coil, and improvement characterized by reduced contact arcing which comprises: a first discharge path including a low resistance connected to discharge said capacitance means through said normally-open contact whereby .the portion of time when the interrupter is engaged with the normally-closed contact is controlled, and a second discharge path including a high resistance bridged across the normally-closed contact to permit the application of power from said power sup ply to said relay coil When the interrupter is in the normally-open position to thereby provide rapid opening of the normally-closed contact and to increase contact pressure at the normally-open contact.

References Cited in the file of this patent UNITED STATES PATENTS 

